The invention relates to a diaphragm control circuit for a camera, and more particularly, to a diaphragm control circuit for a camera including a diaphragm mechanism which is operated through a control of a stepping motor.
Recently, a diaphragm control circuit utilizing a stepping motor is used in cameras of an automatic exposure control type. The stepping motor is interconnected with a diaphragm mechanism so that an angular increment through which the stepping motor rotates is determined in accordance with the amount of reflected light from an object being photographed to thereby control a diaphragm aperture. To assure the accuracy of the angular increment, the rotary shaft of the stepping motor is reversely rotated to its initial position after it has been used to drive the diaphragm mechanism. For example, the stepping motor is returned to its initial position in response to the closure of a shutter, or in response to the operation of a member associated with a film winding mechanism. However, in the prior art construction of the diaphragm control circuit, a design is made such that the stepping motor is left deenergized except when taking a picture in order to achieve a saving in the power dissipation. However, this might cause a displacement of the motor shaft from its initial position in response to extraneous oscillations applied thereto until the next time a picture is taken. Hence, the displacement must be prevented by the provision of a special mechanical constraining member, resulting in a complex arrangement and interfering with the recent trend toward achieving a reduced size of the camera.